As noted in the preceding section, the distribution of luminous matter in the
Universe has the character of soap bubbles and filaments. The following
FIGURE: Data from the survey of galaxies.
The voids and
"walls" that form the large-scale structure are mapped here by 11,000 galaxies.
Our galaxy, the Milky Way,
is at the center. The outer radius is at a distance of
approximately 450 million light-years.
Obscuration by the plane of the Milky Way is responsible for the missing
pie-shaped sectors to the right and left. Click on the image to get a larger
(Smithsonian Astrophysical Observatory, 1993. Northern
data (top)--Margaret Geller and John
Huchra, Southern data (bottom)--Luiz da Costa et al. Quoted in
Cosmology, a Research
Briefing, National Academy of Sciences.)
Computer Simulation of Structure
Here is a link to a
set of MPEG movies showing computer simulations of
large-scale structural growth in the
Universe that uses a mixture of hot and cold
The adjacent image shows the end result of such a simulation.
In this simulation
(Greg L. Bryan and Michael L. Norman,
Grand Challenge Cosmology Consortium),
filaments grow that
eventually exceed 100,000 light years in length and surround gigantic
low-density gas. The intersections of the filaments produce regions of high
density (signified by red) that are thought to generate bright
X-ray clusters of galaxies.
The adjacent image shows a simulation of the growth of structure in the Universe
using cold dark matter.
The void and filament structure is quite noticeable
in this image
Ahead, Warp Factor One, Mr. Sulu!
Here is a corresponding
VRML 3D simulation of filament and soap bubble structure
for the Universe
using cold dark matter
[Note: file is 2.1 MB in length and requires a VRML viewer (e.g., Cosmo
Player).] If you have a VRML viewer, this simulation of a 100 Mpc x 100 Mpc x 100
Mpc cube of the Universe permits you to navigate through the
filament, soap bubble, and void structure described above.
open areas are the voids. The superclusters of
galaxies are the dense clusterings along the filaments, and the brightest spots
in these filaments are the most luminous large clusters.
How Were the Voids Formed?
Any theory of the origin of large scale structure must account for the
formation of voids, which occur on scales of approximately 100 Mpc. We can
immediately place one constraint on their formation. If we take as a
reasonable estimate of a peculiar velocity for a galaxy
~ 600 km/s, it would take 160 billion
years for such a galaxy to travel 100 Mpc and
cross a void - far
longer than the age of the Universe. Therefore, it is extremely unlikely
that the voids were formed by galaxies moving out of a region the size of a
void after their formation. The galaxies must (on the scale set by voids)
have formed near where they are today, so voids must reflect the
distribution of our present galaxies at the time when they were created.